Tools for bending tubes, pipes and conduits are of a well-known type, usually comprising a one-piece body that has an elongated, downwardly grooved arcuate shoe at its bottom, a hook at its front, and an upwardly projecting handle socket in which a handle is removably receivable. The hook is engaged under a length of tubing to be bent, which is held down against a floor or other supporting surface, and bending force exerted upon the handle, transmitted to the tube by means of the hook, curves the tube around the shoe.
With most such tools heretofore available, there was no way of directly determining, during use of the tool, the angle of bend that had been imparted to the tube being bent. Usually, therefore, the user had to terminate the bending operation when he estimated that the desired bend angle had been achieved, then measure the actual bend angle, and then often as not make one or more further bends and measurements until the desired angle had been obtained.
U.S. Pat. No. 2,953,048, issued to J. A. Brown in 1960, disclosed an angle readout device in the form of an accessory for attachment to a bending tool. It was one of several prior attempts to solve the problem to which the present invention is directed, and, like the others, it had marked deficiencies. The device of the Brown patent was detachably secured to the removable handle of the bending tool by means of a clamp that was installed on the handle at a distance above its socket on the tool body. The clamp supported a medially pivoted lever that was swingable relative to the handle and a dial that it held stationary on the handle. One arm of the lever served as a pointer that cooperated with the dial, and the opposite arm terminated in a follower that rested on the tube to be bent, at a location some distance to the rear of the tool body. As the handle of the tool was swung during a tube bending operation, the dial moved with the handle and relative to the lever to provide indications of bend angle. Accuracy of the device was dependent upon accurate location of its clamp both lengthwise and rotationally along the handle, since the location of the lever pivot determined the angle of the follower lever in any given position of the handle. Installing and adjusting the device was thus likely to take more time than could be saved by its use in making a few bends, so that it was actually inefficient for many jobs. Furthermore, its long, freely swingable follower lever made the tool awkward to carry and complicated the engagement of the tool proper with tubing to be bent.
An earlier (1954) U.S. patent to J. W. Lewin, No. 2,666,351, had disclosed a somewhat similar angle indicating attachment for a tube bender, likewise intended to be attached to the handle for the tool. Lewin's device comprised a stop arm that was intended to be locked in any one of a number of designated angle positions and to strike the floor or other supporting surface when a tube bend had attained the angle for which the arm was adjusted. Although less cumbersome than the device of the above-discussed Brown patent, that of the Lewin patent was nevertheless far from compact, and it had the further disadvantage of needing adjustment each time a different angle was to be bent.
U.S. Pat. No. 3,718,018, issued in 1973 to J. D. Benfield, disclosed a bending tool having a step-like series of upper surfaces that were disposed at acute angles to one another, each bearing an indication of bend angle. The tool was operated in the conventional manner, and to produce a bend of a desired angle the handle of the tool was swung until the surface marked with the desired angle of bend was brought to a horizontal orientation. This development was obviously not very satisfactory in actual use because of the extreme difficulty of judging the point at which a relatively small surface, viewed from above, has swung to an exactly horizontal attitude; but the patent demonstrates that the art was seeking a compact indicator, formed integrally with the bender body and having no substantial projections that might be bent or broken under the high forces imposed upon a bending tool both in its use and in other handling.
To avoid the need for judging the attitude of the tube bender body relative to horizontal, U.S. Pat. No. 4,052,881, issued in 1977 to R. W. Mount, disclosed a glass tube that was arcuately curved along its length and was mounted on an upwardly facing surface on the bender body, and a pair of balls that rolled along inside the tube to remain at its lowest point and cooperate with calibrations along the tube for designating the angle of bend that had been achieved. This device was obviously rather expensive, and the glass tube was of course somewhat fragile in relation to the treatment that a bending tool is likely to receive.
A generally similar solution to the problem, with similar deficiencies, is presented by certain commercially available tube benders wherein two spirit levels are mounted on the tool body, at an angle to one another, each oriented to center its bubble when a predetermined bend angle is reached.
A tube bender having an integral angle indicating device is disclosed in U.S. Pat. No. 4,009,602, issued in 1977 to W. A. Linquist. The tube bender of that patent has enjoyed some commercial success, probably because its angle indicating means is sturdy, compact, and accurate enough to be helpful. It comprises small protuberances formed integrally with the body of the bending tool and projecting to one side of the body near the front of it. One of these protuberances, which can be regarded as an upper sighting element, is formed on a reinforcing web that extends forwardly to connect the handle supporting portion of the body with the hook on the front end of the body. Several more such protuberances are formed at intervals along the arcuate shoe at the bottom of the body, to provide lower sighting elements, and there is one more such lower sighting element on the handle supporting portion, intermediate its top end and the shoe. In use, a desired angle of bend is assumed to be achieved when the upper sighting element comes into alignment with a selected one of the lower sighting elements, each of which corresponds to a desired bend angle. A major disadvantage of this indicating device is that the indicated angle of bend will not be the actual angle achieved unless the user's eye is on a line through the upper sighting element that is perpendicular to the surface which supports the tube being bent. If the eye is forward or rearward of the perpendicular line--which shifts rearward with the upper sighting element as the tool is rocked through a bending motion--the selected lower sighting element will come into apparent alignment with the upper one when the actual bend angle is less than or greater than the selected one. Furthermore, judgment of the needed perpendicular is made very difficult by the fact that the user is given only two points to work with and must therefore visualize the line through them as well as estimating its attitude relative to the floor or other supporting surface. The orientation of the handle is of no assistance in this respect, since its axis is spaced to one side of every defined sighting line and is, at best, parallel to only one such line. And, as indicated above, judgment of the perpendicular is further complicated by the confusing rearward migration of the upper sighting element that takes place as the tool is rocked through a bending operation.
It will be apparent from this brief survey of the prior art that the provision of a completely satisfactory bend angle indicator for a tube bending tool has defied not only ordinary skill in the art but also several exercises of inventive ingenuity.